50 



Ths Naturalist. 



The circumstances common to the whole ot a district, which are 

 favourable to the growth of mosses and lichens, are — a pure air, a 

 moist and rainy climate, a hilly and wooded country, and a soil 

 composed of hard ancient rocks. These conditions are generally met 

 with in the west of England, and hence the luxuriance of cryptogams 

 there. The Rev. W. Leighton says : — " The abundance of lichens in 

 a fully developed and fructiferous condition is a sure and certain 

 indication of the purity of the air and salubrity of the climate," 

 Ferns and liverworts like similar conditions ; the latter are especially 

 ."atlantic" in their type of distribution, loving the mild moist 

 equable atmosphere brought by the Gulf Stream to our western 

 coasts. Club-mosses grow on mountainous moors, and horsetails in 

 wet places and shady woods. Cryptogams love to grow 



" Where things that own not man's dominion dwell, 

 And human foot hath ne'er or seldom been." 



Both mosses and lichens, but especially the latter, shrink from man's 

 defilements, though a few mosses, as Tortula muralis and Fimaria 

 liygrometrica maybe found even close to our large towns. In suburban 

 situations we often find tree trunks covered with a green powder, 

 which by some botanists is considered to be an alga, and called 

 Ghlorococcum vulgare, and by others is thought to consist of the 

 gonidia of lichens in a rudimentary state. 



The extension of our railway system is not on the whole favourable 

 to cryptogams, but there is one situation in which they may be 

 frequently found — viz., the dwarf wall which supports the platform : 

 this is out of the way of the smoke, and frequently moistened by the 

 steam escaping from under the engine. Like the "ivy green" of 

 which Dickens sings, they are great lovers of antiquity : an aged 

 tree, an ancient building, or an old exposed rock, will generally be 

 found richly covered with them. In alpine situations, however, rocks 

 which are much exposed undergo too rapid disintegration to afford a 

 favourable foothold to mosses and lichens, and they will consequently 

 be found in greater plenty on the more sheltered and moister aspects. 



Mountains are indeed the favourite home of mosses and lichens ; some 

 large genera are almost confined to such situations. They extend far 

 above the snow-line, and some lichens, as Lecldm geograpJiica, may even 

 be found on sheltered rocks at the summits of the highest Alps ; the 

 larger lateral-fruiting mosses and foliaceous lichens reach their 

 maximum, however, in sub-alpine woods rather than in the higher 

 mountain regions, which are more frequented by acrocarpous mosses 

 and crustaceous lichens. Blocks transported to the plains by glacial 



